Variable cam timing (VCT) is used in engines to advance or retard intake and/or exhaust valve timing. Consequently, intake and/or exhaust valve timing may be adjusted based on engine operating conditions to increase combustion efficiency and decrease emissions, if desired. Additionally, engine power output may be increased across a wider range of engine operating conditions than with fixed valve timing systems.
A locking mechanism, also known as a phase control apparatus, of a VCT system may be configured to lock the VCT system in a desired base configuration when there is insufficient oil pressure to operate the VCT system, such as during engine startup, or during engine idle conditions. Specifically, the locking mechanism may include a locking pin that locks a rotor inside a housing of the phase control apparatus. Backlash and overtravel gaps between components of the locking mechanism, such as between the locking pin and its receiving hole in the housing, are carefully controlled to tight specifications. If backlash or overtravels gaps are too tight, sticking and binding issues may occur between locking components. Conversely, if backlash or overtravel gaps are too large, it may lead to noise, vibration, and harshness (NVH) issues during VCT operation. In some cases, camshaft torque fluctuations can cause the components of the locking mechanism to oscillate within the backlash gaps while in the locked configuration, thereby causing the components to impact each other and causing undesirable noise that may be referred to as knocking.
Other attempts to address NVH issues in VCT systems include methods for setting a locking pin backlash and/or overtravel gap for the locking mechanism that includes either adjusting the backlash during a VCT actuator assembly process or controlling it within tightly controlled tolerances. One example approach for a phase control apparatus is shown by Moetakef et al. in U.S. Pat. No. 9,021,998. Therein, a phase control apparatus is disclosed that includes a locking pin coupled to a vane of a rotor, the locking pin extending into a locking pin recess disposed in a cover plate in a locked configuration. There is locking pin backlash between the locking pin and locking pin recess, as well as VCT overtravel disposed between the vane and housing of the phase control apparatus in order to avoid impact between the vane of the rotor and the housing. Thus, in the locked configuration, a gap exists between the vane including the locking pin and the housing. However, the inventors herein have recognized potential issues with such systems. As one example, controlling the backlash and overtravel during assembly may involve precise measurement techniques that require frequent re-calibration, which may increase the time and cost of assembly. In another example, the backlash and overtravel tolerances may eventually degrade over time with normal wear of locking mechanism components, leading to an increase of NVH issues.
In one example, the issues described above may be addressed by a phase control apparatus for a camshaft including a vane rotor positioned within a housing and including a first vane extending from a central hub; a first chamber formed between walls of the housing and the hub, the first vane arranged within the first chamber; and an isolator pad positioned within a recess of a first wall of the walls and between the first wall and a first sidewall of the first vane. In this way, as the vane rotor is moved to a locked position it may contact the isolator pad, which may be constructed of a rubber or plastic material, without contacting the housing wall, thus reducing the likelihood of metal-to-metal contact. In this way, knocking noises due to metal components hitting one another may be mitigated without having to tightly control natural camshaft torque fluctuations and/or the tight tolerances of backlash and overtravel.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.